Exercise Pressor Reflex Contributes to the Cardiovascular Abnormalities Characterizing: Hypertensive Humans During Exercise

Abstract

We investigated the impact of hypertension on circulatory responses to exercise and the role of the exercise pressor reflex in determining the cardiovascular abnormalities characterizing patients with hypertension. After a 7-day drug washout, 8 hypertensive (mean arterial pressure [MAP] 130±4 mm Hg; 65±3 years) and 8 normotensive (MAP 117±2 mm Hg; 65±2 years) individuals performed single-leg knee-extensor exercise (7 W, 15 W, 50%, 80%-W_peak) under control conditions and with lumbar intrathecal fentanyl impairing feedback from µ-opioid receptor-sensitive leg muscle afferents. Femoral artery blood flow (Q_L), MAP (femoral artery), leg vascular conductance, and changes in cardiac output were continuously measured. While the increase in MAP from rest to control exercise was significantly greater in hypertension compared with normotension, the exercise-induced increase in cardiac output was comparable between groups, and Q_L and leg vascular conductance responses were ≈18% and ≈32% lower in the hypertensive patients (P<0.05). The blockade-induced decreases in MAP were significantly larger during exercise in hypertensive (≈11 mm Hg) compared with normotensive (≈6 mm Hg). Afferent blockade attenuated the central hemodynamic response to exercise similarly in both groups resulting in a ≈15% lower cardiac output at each workload. With no effect in normotensive, afferent blockade significantly raised the peripheral hemodynamic response to exercise in hypertensive, resulting in ≈14% and ≈23% higher Q_L and leg vascular conductance during exercise. Finally, Q_L and MAP during fentanyl-exercise in hypertensive were comparable to that of normotensive under control conditions (P>0.2). These findings suggest that exercise pressor reflex abnormalities largely account for the exaggerated MAP response and the impaired peripheral hemodynamics during exercise in hypertension.

Keywords: blood pressure; cardiovascular disease; exercise; hypertension; reflex.

Figure 1.. Mean arterial pressure (MAP) at rest and during the final minute of each work rate during the control (Ctrl) and fentanyl exercise in hypertensive (HTN) and normotensive (NTN) participants.

There was an effect of HTN on MAP during CTRL (P < 0.05). *P < 0.05 vs. HTN (panel A) and vs. CTRL (panels B and C).

Figure 2.. Heart rate at rest, during the final minute of each intensity, and percent increase in cardiac output from rest during control (Ctrl) and fentanyl exercise in hypertensive (HTN) and normotensive (NTN) participants.

HR was not different between the two groups at the absolute work rates (P = 0.2), but higher in NTN compared to HTN during relative work rates (P < 0.05). The percent increase in cardiac output from rest was not different between the two groups at both absolute and relative work rates during CTRL exercise (P > 0.3). P values on graph indicate main effect of fentanyl. *P < 0.05 vs. CTRL.

Figure 3.. Femoral blood flow, leg vascular conductance, and leg VO₂ at rest and during the final minute of each work rate performed under control (CTRL) and Fentanyl conditions in hypertensive (HTN) and normotensive (NTN) participants.

During CTRL exercise at the same absolute and relative work rates, femoral blood flow, leg vascular conductance, and leg VO₂ were lower in HTN compared to NTN (P < 0.05). P values on graph indicate main effect of fentanyl. *P < 0.05 vs. CTRL.